This application proposes neurophysiological studies to reveal the factors responsible for the normal development of the mammalian central visual system, with particular attention to the role of electrical activity. Previous work has disclosed that the rearrangement of neuronal connections in the normal development of the cat's visual cortex depends on the pattern of impulse activity coming from the eyes. These findings suggest that spontaneous activity of visual neurons, which occurs even in the absence of vision, may play a role in setting up appropriate connections in the central nervous system. Thus abberations in such activity during fetal development may be a hitherto unsuspected cause of birth defects. Electrical stimulation of the optic nerves in developing cats subjected to binocular retinal blockage will be used to characterize the time course of the mechanism that causes geniculocortical afferents serving the two eyes to segregate into ocular dominance patches. The similarity of this 'simplified' model to normal development will be evaluated, and the factors controlling the size of ocular dominance pathces examined. Biophysical and morphological studies will follow. The geniculostriate visual system of the ferret will be studied to characterize intrinsic differences between the monocular and binocular representations. The projections of ON AND OFF channels to the visual cortex will be determined, and W, X, and Y channels sought. These data will suggest rules for the formation of specific connections in the nervous system.